1. Field of the Invention
The present invention relates to a technique for determining a desired intermediate value from a series of signal values, and integrated circuitry that may be used in implementing the technique.
2. Description of the Prior Art
In certain applications, it is desirable to determine the median value of a set of signal (e.g., voltage) values. For example, a disk drive servo control system monitors the position of a pickup head located on a servo arm by measuring the strength of the signal induced in the head by the servo tracks underneath the pickup head. These servo tracks on the disk contain data signals having a defined pattern. As a result of reading the servo control data, a positioning signal is generated to move the servo arm as necessary in order to position the pickup head in the desired location. In the case of a magnetic disk, the pickup head may be a magnetic head, and the signal is induced from the magnetic pattern in the servo tracks. In the case of an optical disk, the pickup head may be an optical transducer of various types, and the tracks may be optical tracks. It is also known to include both two types of signals in a given system, as when an optical pickup is used to position a magnetic readout head.
In one proposed system, the servo control data is obtained from a magnetic head in four bursts of sinusoid signals, with each burst including five sine waves of equal magnitude. It is then necessary to determine the amplitude of the burst. However, the sinusoids within a burst may be corrupted by noise. In order to filter out the noise, one method would be to average the peak values of the five sine waves within a burst. A better method is to determine the median value of the peaks of the sine waves, which is more likely to yield an accurate estimate of the correct value of the sine wave peak when dealing with only a few sine waves. This determination of the median is made for each of the four bursts, in order to yield the desired positioning information. Various other applications also require determining the median value of a set of values, which may be derived from electrical signals or other sources.